Process for producing methionine

Abstract

A process for producing methionine by hydrolysis of 5-(β-methylmercaptoethyl)hydantoin in the presence of an alkali, in which the concentration of hydrogen sulfide is 5 ppm or less in a solution used for hydrolysis comprising 5-(β-methylmercaptoethyl)hydantoin and the alkali, whereby methionine can be stably produced for a long period of time.

1. A process for producing methionine comprising the step of:
 reacting methyl mercaptane with acrolein to obtain 3-methylmercaptopropionaldehyde, 
 subjecting 3-methylmercaptopropionaldehyde to cyanhydrination with hydrogen cyanide to obtain 3 -methylmercaptopropioncyanhydrin, 
 subjecting 3 -methylmercaptopropioncyanhydrin to hydantoination using carbon dioxide and ammonia to obtain 5-(β-methvlmercaptoethyl)-hydantoin, and 
 hydrolyzing 5-(β-methylmercaptoethyl)hydantoin in the presence of an alkali, 
 wherein a concentration of hydrogen sulfide is lowered to 5 ppm or less in a solution used for hydrolysis comprising 5-(β-methylmercaptoethyl)hydantoin and the alkali by at least one of the following methods:
 1) distillation or rectification of the solution comprising 5-(β-methylmercaptoethyl)hydantoin and the alkali; 
 2) use of an excessive amount of acrolein relative to methyl mercaptane during the reaction of methyl mercaptane with acrolein; 
 3) addition of a substance for removing hydrogen sulfide. 
 
 
     
     
       2. The process according to  claim 1 , which further comprises a step of measuring the concentration of hydrogen sulfide in the solution used for hydrolysis comprising 5-(β-.methylmercaptoethyl)hydantoin and the alkali and adjusting the concentration of hydrogen sulfide in the solution to 5 ppm or less, prior to the use of the solution for hydrolysis.